The ElarmS methodology is designed to predict the distribution of peak ground shaking across the region affected by an earthquake before the beginning of significant ground motion at the epicenter. The method uses the first few seconds of the P-wave at the stations closest to the epicenter to estimate the magnitude of the earthquake. Attenuation relations provide the predicted distribution of ground shaking as a function of distance from the epicenter (Allen, 2004). The complete ElarmS system generates an "AlertMap" of predicted peak ground shaking. The first AlertMap is available 1 sec after the first P-wave trigger and is updated every second as additional data is gathered from stations further from the epicenter.
More information about ElarmS is available at http://www.ElarmS.org.